The present invention generally relates to semiconductor fabrication and connection methods and apparatus, and more particularly to fabrication and connection methods and apparatus high voltage semiconductor power switching devices that are useful in ignition exciters for turbine engine applications.
Modern turbine engine ignition exciters, especially those used in small gas turbine applications, have evolved considerably in recent years; migrating from spark gap (plasma) switching devices and simple relaxation type oscillator charge pumps to more reliable and predictable solid state switching devices with digitally controlled DC-DC converter charge pumps. Thermal performance of current art solid state ignition exciters has been limited due to available thyristor switching technology. Some designs use multiple series stacked phase control thyristors with saturable reactors, while others employ switching devices specifically designed for pulse power applications. However, performance of both suffer from leakage current related limitations of the switching devices. At elevated temperatures, leakage current within the switching device results in increased power dissipation. This condition precipitates additional leakage current, resulting in a thermal runaway condition and device failure.
The most advanced current art exciters employ pulse type thyristors to eliminate the need for saturable magnetic components in the output stage and the associated limitations of that technology. While a considerable improvement over phase control based designs, thermal performance of current art pulse thyristor based ignition exciters is still limited by switching device leakage current. Moreover, current art technology incorporates costly semiconductor die manufacturing and device packaging techniques limiting commercial viability of the ignition exciters.
The ignition exciter embodiments in the above referenced Wilmot et al. application utilize a semiconductor pulse switching device that is designed to exhibit low leakage current at elevated ambient temperatures. It has a design configuration that is disclosed in the Wilmot et al application and in above referenced Driscoll et al. patent application. The design configuration also facilitates the use of novel fabrication and mounting processes and apparatus which greatly reduces the cost of manufacturing and connecting the semiconductor pulse switching device in an exciter product.